In this lesson, you will learn about two similar grammatical principles and their (similar) respective meanings. In this lesson, you will learn how to use ~아/어서는 안 되다 to mean “one should not” and ~(으)면 안 되다 to mean “one must not.” We will also look at the positive meaning of using ~(으)면 되다, which is a very natural expression but usually one that foreign learners of Korean don’t use right away. Let’s get started.

One should not: ~아/어서는 안 되다

In Lesson 49, you learned how to apply 되다 to many different types of sentences. In addition to the meanings introduced in Lesson 9 and Lesson 14, you learned that 되다 can be used to indicate that there is “no problem” with something. For example:

You also saw that this can be applied to sentences with ~아/어도 to indicate that there is “no problem” with an action being done. You might remember, the most common translation for these types of sentences was “one may” or “one can.” For example:

지금 문을 열어도 돼요 = You may open the door now제일 편리한 것을 선택해도 돼요 = You may choose the most convenient one
그 파일을 저의 컴퓨터에 저장해도 돼요 = You can store/save that file on my computer

Attaching ~아/어서는 안 되다 to the end of a clause indicates that there will be a problem if the action is completed. This type of sentence is essentially the opposite of the type of sentence above. Now, instead of indicating that there will not be a problem, (by just using 되다) we are indicating that there will be a problem (by using 안 되다). The typical English translation of this is usually “one should not.” For example:

Even though these sentences are used in the present tense, they are usually referring to actions that occurred in the past (unless somebody is just making a general statement that “one should not” do some action). For example, in the first example above:

You can use “안 되다” after “~(으)면 to indicate that there will be a problem when/if a something occurs. For example:

그렇게 하면 안 돼요 = You must not do it like that

This meaning is very similar to the meaning learned above (~아/어서는 안 되다), but I like to think that the meaning is slightly stronger when you use ~(으)면 안 되다. Below are more examples:

그 정보를 누락하면 안 돼요 = You must not omit that information
그 말을 영어로 하면 안 돼요 = You must not say that in English
이 차에 디젤을 넣으면 안 됩니다 = You must not put diesel fuel in this car
그런 말을 유아에게 하면 안 돼요 = You must not say that type of thing to a child
현재오염문제를 무시하면 안 돼요 = You must not ignore the current pollution problem
정서장애가 있는 친구들을 놀리면 안 돼요 = You must not pick on friends with emotional disabilities
주어를 그 문장에서 그 위치에 쓰면 안 돼요 = You must not use the subject in that place in a that sentence

~(으)면 안 되다 is often used in the form of a question. When used as a question, one is asking if there will be a “problem” if the action before ~(으)면 occurs. It is possible to translate these types of sentences to English in many ways, which I have provided. For example:

이렇게 하면 안 돼요?
= Can’t you do it like this?
= Are you able to do it like this?
= Is it okay if you do is like this?
= Will there be any problem if you do it like this?

더 빨리 하면 안 돼요?
= Can’t you do it faster?
= Are you able to do it faster?
= Is it okay if you do it faster?
= Will there be any problem if you do it faster?

조금 더 주면 안 돼요?
= Can’t you give me a little bit more?
= Are you able to give me a little bit more?
= Is it okay if you give me a little bit more?
= Will there be any problem if you give me a little bit more?

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It is also possible to create a double negative with this type of question. For example, if you wanted to ask if you could eat now, you could say:

밥을 지금 먹으면 안 돼요?
= Can’t we eat now?
= Are we able to eat now?
= Is it okay if we eat now?
= Will there be any problem if we eat now?

However, by making the original action negative, the speaker can ask if it is alright if something is not done. For example:

밥을 지금 안 먹으면 안 돼요?
= Can we not eat now?
= Are we able to not eat now?
= Is it okay if we don’t eat now?
= Will there be any problem if we don’t eat now?

Other examples:

그 대회를 참여하지 않으면 안 돼요?
= Can we not participate in that event?
= Are we able to not participate in that event?
= Is it okay if we don’t participate in that event?
= Will there be any problems if we don’t participate in that event?

이번에 여행할 때 수천 장의 사진을 찍지 않으면 안 돼요?
= Can you not take thousands of pictures this time when we travel?
= Are you able to not take thousands of pictures this time when we travel?
= Is it okay if you don’t take thousands of pictures this time when we travel?
= Will there be any problem if you don’t take thousands of pictures this time when we travel?

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This form is actually a very polite way to ask for something to be done. As such, it is common for ~아/어 주다 (Lesson 41) to be used with the question version of ~(으)면 안 되다. For example:

밥을 사 주시면 안 돼요?
= Are you able to buy me rice?
= Is it okay if you buy me rice?

교통카드를 충전해 주면 안 돼요?
= Are you able to charge my subway card?
= Is it okay if you charge my subway card?

If you ask somebody a question like this (or any other question asking if something can be done), the answer that is typically given when it cannot be done is “안 돼요.” For example:

You can also use the form ~(으)면 안 되다 without “안” to create a different meaning. I will talk about this next.

Suggesting that one should: ~(으)면 되다

By adding ~(으)면 되다 to the end of a sentence or clause, you create a meaning that is very similar to ~아/어야 하다, which you learned in Lesson 46. This form has the meaning of “you must” or “you should” depending on the situation. For example:

서울역에서 내려야 돼요 = You must/should get off at Seoul station

Using ~(으)면 되다 creates a similar meaning. For example:

서울역에서 내리면 됩니다 = You should get off at Seoul station

Here, the speaker is basically indicating “it/everything will be okay if you get off at Seoul station.” Although the meaning is similar to ~아/어야 되다, using ~(으)면 되다 is more of a suggestion. Because this is more of a suggestion, its meaning is very soft and is often used by people when they are asked for advice. For example, one time a woman asked my wife how to get to 사당 station, to which my wife replied:

다음 역에서 내리면 돼요
= You can/should get off at the next station
= There will be no problem (it will be okay) if you get off at Seoul Station

A more natural translation could sometimes be “one can.” For example:

조금만 넣으면 돼요 = Just put a little bit in
조금 더 올라가면 돼요 = Just keep going up a little bit further
코피를 휴지로 막으면 돼요 = You can block the nosebleed with a tissue
소금을 얼마나 더 넣어야 돼요? = How much more salt should I put in?
애기가 피곤하면 업어 주면 돼요 = If the baby is tired, you can carry him on your back